Study on dynamic mechanical properties and mesoscopic simulation of steel-polyoxymethylene hybrid fiber reinforced concrete

To reveal the dynamic mechanical properties and meso-damage characteristics of steel-polyoxymethylene hybrid fiber reinforced concrete (HFRC).In this study, the Split Hopkinson Pressure Bar (SHPB) tests were conducted to investigate the dynamic mechanical properties of plain concrete (PC), steel fiber reinforced concrete (SFRC), and HFRC. Scanning electron microscopy (SEM) was employed to observe the micromorphology and fracture characteristics of the fiber-matrix interface. A three-dimensional mesoscopic numerical model was established using LS-DYNA software, which incorporated polyhedral aggregates, mortar, interfacial transition zone (ITZ), and two types of fibers. The damage evolution, energy dissipation, and stress characteristics of HFRC were revealed from a mesoscopic perspective. The results show that polyoxymethylene (POM) fiber exerts a synergistic reinforcing effect with steel fiber, significantly improving the dynamic impact resistance of the material. Specifically, steel fiber exhibits strong bonding with the matrix and dissipates energy via interfacial slip, whereas POM fiber presents weak interfacial bonding and dissipates energy mainly through pull-out, fracture, and deformation. The two fibers function synergistically at different stages of crack propagation, effectively enhancing the crack resistance and energy dissipation capacity of the matrix. Meso-simulations indicate that mortar serves as the primary energy-dissipating component, and ITZ is the weakest region that fails first under impact loading. With increasing impact air pressure, the energy absorption and peak stress of each component increase significantly. Hybrid fibers can reduce energy reflection and kinetic energy loss, facilitating more impact energy to be absorbed and dissipated. The peak stress of ITZ is the most sensitive to loading rate, while aggregate shows the lowest sensitivity. The established mesoscopic model can well reproduce the dynamic mechanical behavior and damage characteristics of HFRC, providing theoretical and numerical references for the application of HFRC in impact-resistant engineering.